1. Field of the Invention
The present invention relates to a print head for a piezoelectric ink jet printer, and more particularly to such a print head including a laminated piezoelectric actuator. The invention also relates to a piezoelectric actuator in the form of a plate for such a print head, and to a process for producing such actuators.
2. Description of the Related Art
U.S. Pat. No. 5,402,159 discloses a print head for a piezoelectric ink jet printer. The print head includes a cavity plate and a piezoelectric actuator in the form of a laminated plate. The cavity plate has nozzles and pressure chambers. The pressure chambers are open on one side of the cavity plate, and each communicate with one of the nozzles. The piezoelectric actuator includes piezoelectric sheets, sets of drive electrodes and some common electrodes. The drive electrodes and common electrodes are interposed between the piezoelectric sheets. Each set of drive electrodes is associated with one of the pressure chambers. The common electrodes are common to all the pressure chambers. The cavity plate lies on the piezoelectric actuator in such a manner that the actuator closes the pressure chambers.
As shown in FIGS. 11 and 15 of the foregoing patent, the piezoelectric actuator also includes side electrodes formed on side faces of it. Each side electrode is connected electrically to one of the sets of drive electrodes, and can be connected electrically to the outside. The side electrodes may come into contact with the cavity plate, which lies on the piezoelectric actuator. If the cavity plate is metallic, the contact short-circuits the side electrodes.
In order to prevent such short circuits, another conventional art of this type includes a cavity plate made of an alumina ceramic, which is an electrical insulator, or other non-conducting material. However, this cavity plate becomes larger in order to ensure a predetermined strength of the cavity plate. In addition, the material cost for the cavity plate is higher, and the processing steps for it becomes more complicated. As a result, the cost of the cavity plate is considerably higher.
Still another conventional art provides an insulating sheet between a cavity plate and a piezoelectric actuator in order to avoid the short circuit therebetween. The interposition of the insulating sheet allows the cavity plate to be made of metallic. The metallic cavity plate can be smaller and less costly than the cavity plate made of an alumina ceramic or other non-conducting material. However, the interposition of the insulating sheet increases the number of parts for the print head. The increased number of parts prevents the print head from being sufficiently small and inexpensive. In addition, the interposition of the insulating sheet increases the number of places where ink may leak.
In the foregoing patent, the side electrodes are formed on the side faces of the piezoelectric actuator by vacuum metallizing, metal spattering, conductive paste coating, or the like. The side electrodes rise slightly from the side faces. Consequently, while the piezoelectric actuator is produced or assembled, the side electrodes are very liable to be damaged by a handler, a jig or the like coming into contact with them. This causes defectives to be produced at a higher rate while piezoelectric actuators are produced.
It is an object of the present invention to provide an ink jet printer print head including a cavity plate and a piezoelectric actuator which lie on each other, the actuator including side electrodes provided on side faces of it and kept out of contact with the cavity plate without an insulating sheet interposed between the actuator and cavity plate.
It is another object to provide a piezoelectric actuator for an ink jet printer print head, the actuator including side electrodes provided in side faces of it without rising or protruding from them.
It is still another object to provide a process for producing such piezoelectric actuators at a low cost.
In accordance with a first aspect of the present invention, a print head is provided for a piezoelectric ink jet printer. The print head includes a piezoelectric actuator in the form of a plate. The actuator includes a piezoelectric sheet having a first face and a second face which are opposed to each other, and a side face connecting therebetween. The actuator further includes a common electrode lying on the first face of the piezoelectric sheet, a number of drive electrodes lying on the second face of the sheet, and side electrodes formed on the side face of the actuator. The common electrode lies over the drive electrodes. The side electrodes are each connected to one of the drive electrodes or one of the common and drive electrodes. The print head further includes a cavity plate having pressure chambers open on one side of the plate, nozzles each communicating with one of the chambers, and a recess formed on the one side. The actuator lies on the one side of the cavity plate in such a manner that the actuator closes the pressure chambers. The drive electrodes are each aligned with one of the chambers. The side electrodes are aligned with the recess to be kept out of contact with the cavity plate.
Thus, the recess of the cavity plate makes it possible to reliably keep the side electrodes of the piezoelectric actuator out of contact with the plate without interposing an insulating sheet between the plate and actuator. This enables the cavity plate to be metallic. It is consequently possible to reliably make the print head smaller and cheaper without increasing the number of places where ink may leak.
The piezoelectric actuator may further include outer electrodes formed on a surface of the actuator which is opposed to a surface of the actuator covering the one side of the cavity plate. The outer electrodes are each connected to one of the side electrodes. This simple actuator structure makes it possible to connect the outer electrodes reliably to the wiring patterns of a flexible flat cable for connection to external apparatus or equipment by pressing the cable against that surface of the piezoelectric actuator on which the outer electrodes lie.
The piezoelectric actuator may further include a second piezoelectric sheet lying on the first piezoelectric sheet and a third piezoelectric sheet lying on the one side of the cavity plate. The first piezoelectric sheet lies between the second and third piezoelectric sheets. The common electrode lies between the first and second piezoelectric sheets. The drive electrodes lie between the first and third piezoelectric sheets. The outer electrodes lie on the second piezoelectric sheet.
The recess of the cavity plate may be a groove extending along the side surface of the piezoelectric actuator. The groove for all the side electrodes is less costly to form than recesses for the respective side electrodes.
The cavity plate may include a base sheet lying on the one side. The recess may be a slot punched in the base sheet.
In accordance with a second aspect of the present invention, a piezoelectric ink jet printer print head is provided. This print head includes a cavity plate having a plurality of nozzles and pressure chambers each communicating with one of the nozzles, and an actuator lying on one side of the cavity plate. The actuator includes a piezoelectric sheet having a first face and a second face opposed to the first face and a side face connecting the fist and second faces. The side face has recesses formed thereon. The actuator further includes drive electrodes, a common electrode and side electrodes. The drive electrodes lie on the second face of the piezoelectric sheet, and are each exposed in one of the recesses. The drive electrodes are each aligned with one of the pressure chambers. Each side electrode is formed in one of the recesses, and connected to the drive electrode exposed in the associated recess. The common electrode lies on the first face of the piezoelectric sheet over the drive electrodes.
Because the side electrodes are positioned in the recess, they do not rise or protrude from the third side of the piezoelectric actuator. Consequently, while the actuator of the printer is produced or assembled, it is possible to reliably reduce the liability of the side electrodes to be damaged by a handler, a jig or the like coming into contact with them.
This piezoelectric ink jet printer may further include outer electrodes formed on a surface of the actuator which is opposed to a surface of the actuator covering the cavity plate. The outer electrodes are each connected to one of the side electrodes. This simple actuator structure makes it possible to connect the outer electrodes reliably to the wiring patterns of a flexible flat cable for connection to external apparatus or equipment by pressing the cable against that side of the piezoelectric actuator on which the outer electrodes lie.
The piezoelectric actuator may further include an insulating sheet and a second piezoelectric sheet. The insulating sheet lies on the first piezoelectric sheet. The second piezoelectric sheet lies on the one side of the cavity plate when the actuator lies on the one side. The first piezoelectric sheet lies between the insulating sheet and the second piezoelectric sheet. The common electrode lies between the insulating sheet and the first piezoelectric sheet. The drive electrodes lie between the first-mentioned and second piezoelectric sheets. The outer electrodes lie on the insulating sheet.
In accordance with a third aspect of the present invention, a piezoelectric actuator is provided, which is in the form of a plate for a piezoelectric ink jet printer print head including a cavity plate on which the actuator is placed. The cavity plate having a plurality of nozzles and pressure chambers each communicating with one of the nozzles, the actuator comprises: a piezoelectric sheet having a first face and a second face opposed to the first face and a side face connecting the first and second faces, the side face having recesses formed thereon; drive electrodes lying on the second face of the piezoelectric sheet and each exposed in one of the recesses, the drive electrodes being each aligned with one of the pressure chambers; side electrodes each formed in one of the recesses and each connected to the drive electrode exposed in the associated recess; and a common electrode lying on the first face of the piezoelectric sheet over the drive electrodes.
In accordance with a fourth aspect of the present invention, a process for producing piezoelectric actuators for piezoelectric ink jet printer print heads is provided, which comprises the steps of:
providing a first green sheet including at least two first matrices defined on both sides of a first boundary;
forming drive electrodes in each of the first matrices on one side of the first green sheet in such a manner that each of the drive electrodes crosses the first boundary;
providing a second green sheet including at least two second matrices defined on both sides of a second boundary;
forming a common electrode in each of the second matrices on one side of the second green sheet in such a manner that the common electrode crosses the second boundary;
joining the two green sheets together to form a laminate in such a manner that the other side of one of the sheets lies on the one side of the other sheet, that the first and second boundaries are aligned with each other;
making a through hole on first and second boundaries in the laminate;
cutting the laminate along the boundaries to separate the matrices of each of the green sheets from each other and divide the through hole into two recesses; and
forming a side electrode in each of the recesses in such a manner that the side electrode is connected to the associated drive electrode.
The process makes it possible to form recesses in side faces of piezoelectric actuators simply by making through holes, and to produce two or more piezoelectric actuators at the same time. It is consequently possible to produce piezoelectric actuators at low cost.
The process may further comprises the steps of: providing a third green sheet including at least two third matrices defined on both sides of a third boundary; and forming outer electrodes in each of the third matrices on one side of the third green sheet in such a manner that each of the outer electrodes corresponds to one of the driving electrodes; wherein, in the joining step, the first, second and third green sheets may be joined together to form the laminate in such a manner that the other side of the third green sheet lies on the one side of the second green sheet, and that the first, second and third boudoirs are aligned with each other, and in the forming step of the side electrode, the side electrode in each of the recesses may be formed in such a manner that the side electrode is connected to the associated drive electrode and the associated outer electrode.
In accordance with a fifth aspect of the present invention, a process for producing piezoelectric actuators for piezoelectric ink jet printer print heads is provide, which comprises the steps of:
providing a first green sheet including at least two first matrices defined on both sides of a first boundary;
forming drive electrodes in each of the first matrices on one side of the first green sheet in such a manner that each of the drive electrodes crosses the first boundary;
providing a second green sheet including at least two second matrices defined on both sides of a second boundary;
forming a common electrode in each of the second matrices on one side of the second green sheet in such a manner that the common electrode crosses the second boundary;
joining the two green sheets together to form a laminate in such a manner that the other side of one of the sheets lies on the one side of the other sheet, that the first and second boundaries are aligned with each other;
making a through hole on first and second boundaries in the laminate;
filling an electrically conductive paste into the through hole in such a manner that the paste is connected to the drive electrodes;
drying the filled paste; and
cutting the laminate along the boundaries to separate the matrices of each of the green sheets from each other, divide the through hole into two recesses, and divide the dried paste into two side electrodes each in one of the recesses.
The process of the fifth aspect may further comprises the steps of: providing a third green sheet including at least two third matrices defined on both sides of a third boundary; and forming outer electrodes in each of the third matrices on one side of the third green sheet in such a manner that each of the outer electrodes corresponds to one of the driving electrodes; wherein, in the joining step, the first, second and third green sheets may be joined together to form the laminate in such a manner that the other side of the third green sheet lies on the one side of the second green sheet, and that the first, second and third boudoirs may be aligned with each other.
This process makes it possible to produce piezoelectric actuators at lower cost than the process of the fourth aspect, which includes the step of forming side electrodes after cutting the laminate.
In each of the processes according to the fourth and fifth aspects, the step of forming outer electrodes may include forming a narrow electrode pattern on the one side of the third green sheet in such a manner that the pattern extends along the third boundary and connects the outer electrodes together. The process may further comprise the step of forming metal skins on the outer electrodes by electroplating these electrodes with an electric current applied to them via the electrode pattern. This pattern is removed at the same time that the laminate is cut. This makes it possible to produce, at low cost, piezoelectric actuators each for improved electric connection with a flexible flat cable.
Thus, by electroplating the outer electrodes with an electric current applied to them via the electrode pattern connecting them electrically together, it is possible to form metal skins, which may be gold, simultaneously on the outer electrodes. This makes it possible to improve the electric connection of the outer electrodes of each piezoelectric actuator with a flexible flat cable reliably without greatly raising the cost of production. At the same time that the laminate is cut, the electrode pattern is removed to electrically insulate the outer electrodes from each other and the side electrodes from each other.